Its fairly self exclamatory. One targets the device, and would effect any user at a device level if applicable and the other targets a specific user. The catch with user level configuration profiles, is the user must be an MDM enabled user for the configuration profiles to work.
Becoming MDM enabled is not as easy to attain as it should be, and device level covers about 99% of configuration profiles so most work flows dont bother with user level anymore. Some user level configuration profiles would be something like a User ADCS certificate.
There's also a difference in installation times with Computer Level and User Level profiles. A device level profile will usually install within seconds (if you're not deploying a large batch at once) while a User Level profile can take considerably longer as it seems to be triggered much less frequently, and most reliably coincides with the jamf binary doing either a policy check or recon..
That explanation makes since. I wonder if the difference also lies in a profile being installed once only or once per user on a shared device.
I needed to re-enable fast user switching and found that the user level was needed for this. The second user didnt have the feature when the profile was at computer level.